Rainfall and runoffThe eastern Tennessee Valley received 4.5 inches of rain in the month of January, which is about normal. Runoff was 3.8 inches, which is slightly above normal.

Runoff is important to reservoir elevations because it is a measure of the water that reaches the river system when it rains instead of being absorbed into the ground. Runoff is affected by soil conditions and by the intensity, amount, and duration of rainfall.

For the past four months, rainfall was 3.6 inches above normal, and runoff was 5.7 inches above normal.

Reservoir elevationsMost reservoirs in the TVA system are higher than normal for this time of year due to heavy runoff from rain and snowmelt and TVA efforts to temporarily store the extra water to reduce downstream flood damage. Main-river reservoirs are near summer elevations, except for Nickajack and Wilson which are within their seasonal operating zones. Tributary reservoirs are almost four feet above their targeted seasonal elevations, on average, as shown in the chart below.

Reservoir

Observed Elevation

Feb. 8
Flood Guide
Elevation*

Feb. 8, 2010

Feb. 8, 2009

South Holston

1708.5

1709.3

1708

Watauga

1951.7

1945.5

1952

Cherokee

1048.3

1045.7

1045

Douglas

961.2

954.7

954

Fontana

1659.3

1654.5

1653

Norris

1006.2

1001.3

1000

Chatuge

1919.6

1918.3

1918

Nottely

1764.1

1762.5

1762

Hiwassee

1494.5

1485.6

1485

Blue Ridge

1672.8

1669.7

1669.7

Tims Ford

879.9

874.3

876.1

Normandy

866.6

865

864

Flood guide levels show the amount of water storage available in the reservoir to help with flood damage reduction during different times of the year. During the winter, TVA’s goal is to keep the reservoir level at the dam from rising above the flood guide to be ready for large rains that could cause flooding. During the summer, the primary objective is to keep reservoir levels as close to the flood guide level as possible to support recreation. In summer, reservoir levels fall below the flood guide only when rainfall and runoff are insufficient to meet downstream flow requirements.

“This year is beginning like last year ended, with a lot of precipitation,” said Chuck Bach, TVA General Manager for River Scheduling. “During the last three months of 2009, rainfall and runoff totals were significantly above normal, and now in 2010 we are getting a significant rain or snow every week. We’ve run the hydroelectric turbines at TVA dams at maximum capacity to move all that water through the system so we’d have room to store additional rain. But, with all of the recent rain and snow, inflows have been so high, we haven’t been able to release the water through the turbines fast enough to recover all the storage space needed. We’ve also had to spill water at all main-river and some tributary power dams in the TVA system to bring reservoir levels down so we’ll be ready if we get more rain in the weeks ahead.”

TVA tries to avoid spilling, according to Bach. “Hydro is our most efficient and economical power source, so we try to release as much water as we can through the turbines at our dams. But our number-one priority is providing the flood-reduction benefits that the TVA system of dams and reservoirs was built to provide. That means spilling water if necessary to ensure that we have adequate flood-storage space.”

All nine hydroelectric dams on the Tennessee River and most of the 20 power-producing tributary dams have been running at maximum power generating capacity. Those dams have generated 7,958 gigawatts of power in the past four months, compared to a normal generation of 5,853 gigawatts.

Bach says TVA already is looking ahead to the spring fill. “In the weeks ahead, we’d like to keep reservoir elevations from dropping below flood-guide levels so that, when the spring fill starts in mid-March, we’ll be in a good position to reach summer target levels on schedule. If the rain continues, that shouldn’t be difficult.”

In answer to your question: Wouldn’t it be a good idea to hold on to some of the rain we get this winter to help fill reservoirs to full pool this summer?
Although holding on to extra rain would help the spring fill, TVA River Scheduling Manager Chuck Bach says TVA must be very careful about going above winter flood-guide elevations.

“Summer storms typically affect only a portion of the Valley, but winter storms can cover the entire Valley for several days, with one storm followed by another even larger storm three to five days later. History provides clear evidence of this pattern. During the past 140 years, the largest flood events occurred in March 1867, February-March 1875, April 1886, March 1897, March 1917, January-February 1957, March 1963, March 1973, April 1977, May 1984, February-March 1994, and May 2003. Plus, runoff is higher in the winter and early spring because vegetation is dormant and the ground is wetter.

“As we get closer to March, we’ll start looking at the possibility of holding more water in the tributary system to help reach June 1 levels. But holding extra water in reservoirs already at flood-guide levels isn’t an option.

“If we were to go above flood guide levels and then got hit by a major winter storm and didn’t have the flood storage space we need, we’d be getting calls from people with water in their homes and businesses and from members of Congress who hold us responsible for operating the reservoir system for the purposes it was built—to improve navigation and reduce flood-damage.”

Dam safety modificationsTVA is raising the elevation of some of its dams to help reduce the chance of flooding in the unlikely event of a worst-case winter rain event.

Temporary, wall-like structures have been installed on top of four dams—Cherokee, Fort Loudoun, Tellico, and Watts Bar—increasing their effective height to prevent water from overtopping and damaging the structures should such an event occur.

TVA River Scheduling Manager Chuck Bach says a recent update of TVA’s river modeling program determined that a worst-case storm could produce more rain than the dams could handle, even with the floodgates wide open. Such an event is highly unlikely. But, because it is possible, federal guidelines and nuclear operating regulations require TVA to be prepared for it.

TVA evaluates its river modeling program regularly as modeling technology evolves and more or better data becomes available. Factors affecting the most recent evaluation included improved modeling technologies and data, alterations to TVA dams, and changes in TVA’s reservoir operating policy since the last evaluation.

Additional analyses are being conducted to determine if other dams need to be modified. Permanent solutions will be developed with public input under the guidelines of the National Environmental Policy Act.

Update on Blue Ridge Dam rehabilitation projectOn Friday, January 8, TVA released the Environmental Assessment and Finding of No Significant Impact related to the Blue Ridge Dam Rehabilitation project.

The project is required to meet new, more rigorous dam safety standards at Blue Ridge Dam. It includes repairs to the penstock (the underwater pipe that carries water from the reservoir to the turbines in the powerhouse), which was damaged the first time it was filled with water in 1931, and modifications to the base of the intake tower and the upstream and downstream faces of the dam to increase seismic stability.

A deep drawdown is required to safely install a new liner in the penstock. The reservoir will be drawn down gradually beginning in mid-July 2010 and held at an elevation about 68 feet lower than the usual summer elevation for about six months.

TVA looked at beginning the drawdown later in the year, but the earlier date was chosen for two reasons: to reduce the risk of rain events adversely impacting the proposed project schedule and to increase the chance of completing the work in a timely manner and successfully refilling Blue Ridge Reservoir in 2011.

The penstock repairs will eliminate the need for regularly scheduled, routine deep drawdowns, currently required about every five years for dam safety inspections due to the deteriorating condition of the penstock.

Get more information on TVA.comThe links below will take you to reservoir-related information on TVA’s Web site.

TVA’s reservoir operating policy: Learn how TVA manages the flow of water through the Tennessee River system to provide navigation, flood damage reduction, power supply, water quality, water supply, recreation, and other benefits.
Reservoir information: Get detailed information about individual reservoirs, including observed and predicted elevations and releases at TVA dams, reservoir operating guides, water quality improvements, fish population survey results, and more. To check reservoir information from your cell phone or other mobile device, go to http://m.tva.com.
Rainfall and stream flows: Get the latest information on daily rainfall and stream flows across the Valley.
Recreation release schedules: View the 2010 schedule for water releases for rafting, kayaking, and canoeing below these TVA dams: Apalachia, Ocoee No. 1, Ocoee No. 2, Ocoee No. 3, Norris, Watauga/Wilbur, and Tims Ford.
Map of TVA reservoirs and power plants: Our interactive map is your guide to the entire TVA power system, including fossil and nuclear plants, dams and reservoirs, and visitor centers. You’ll find interesting facts about each facility and learn how they work together for the purposes of power supply, river management, and economic development.
Water supply FAQs: Get answers to frequently asked questions about obtaining a water intake permit, improving water quality around intakes, inter-basin transfers, and more.
Dangerous areas around TVA dams: If you like fishing or enjoy swimming and boating on TVA-managed reservoirs, you need to be aware of the possible hazards around dams, locks, and powerhouses.
How to lock through: Find out what you need to do to safely approach a navigation lock, secure your boat in the lock chamber, and exit the lock.
Reservoir health ratings: See the latest monitoring results for TVA-managed reservoirs.
Campgrounds and day-use areas: Get information here about campground fees and amenities as well as picnic pavilion reservations.
TVAkids.com: TVA’s got a Web site just for kids! Learn about how TVA makes electricity, reduces flood damage, protects wildlife, and more. There’s a section for teachers, too.
TVA Heritage: Read about the people who founded TVA, shaped its purpose, and built its power plants. TVA Heritage offers fascinating glimpses of the agency’s 76-year history.

Get more information by phone
For the latest information on reservoir elevations and stream flows, call TVA’s Reservoir Information Line from a touch-tone phone:

From Knoxville, TN: 865-632-2264

From Chattanooga, TN: 423-751-2264

From Muscle Shoals, AL: 256-386-2264

From all other locations: 800-238-2264 (toll-free)

For answers to questions on how your reservoir is operated, call TVA River Operations at 865-632-6065.
For answers to questions about recreation, permitting procedures, reservoir land management plans, and other environmental issues, call TVA’s Environmental Information Center at 1-800-882-5263.